The objective of the biophysical nuclear magnetic resonance (NMR) program is the elucidation of the mechanisms by which chemicals and heavy metals present in the environment cause cell injury. The development and application of NMR methodology in order to achieve this objective may be considered to fall into two broad categories: 1) In vivo metabolic analysis using NMR spectroscopy. Such studies probe directly the metabolism of various xenobiotics when sufficient concentrations are present to permit detection. Additionally, studies of the effects of these agents on metabolic parameters thought to play an important role in the mediation of cell injury are carried out. In addition to measurements of intracellular pH and levels of high energy phosphate compounds, current emphasis is on the measurement of free intracellular calcium levels and on the development of fluorinated NMR active spin traps for the in vivo detection of intracellular free radicals. Cellular calcium levels are measured using a fluorinated calcium chelate in combination with 19F NMR detection. Measurements have been carried out in a variety of cell and perfused organ systems, with current emphasis on red blood cells in which fluorescent calcium sensitive dyes cannot readily be used, and in the perfused heart. Efforts are in progress to develop more specific and sensitive probes for calcium and other cellular cations. 2) In vitro studies of the interaction of various chemicals with known or proposed biological targets. Recent studies have involved the use of 13C labeled antifolate drugs, particularly (2-13C) methotrexate, with the enzyme dihydrofolate reductase. Studies of the biosynthesis of tabtoxin, an inhibitor of glutamine synthetase produced by Pseudomouos syringal, have also been carried out.